Sexes are separate in most limpets.  Spawning occurs in late winter/springtime in most species, and development leads to a free-swimming, non-feeding veliger larva. 

NOTE  sex ratios in limpets are rarely mentioned.  In one study on Lottia limatula at Palos Verdes, California a ratio of 1.7 male: 1 female is reported (in 486 specimens).  Seapy 1966 Veliger 8: 300.

Studies on Lottia digitalis at Friday Harbor Laboratories, Washington using specimens from the San Juan Islands and Oregon reveal a developmental pattern that is probably typical for most limpet species on this coast.  Lottia digitalis broadcast-spawns its eggs in winter and these develop into swimming trochophore larvae within 15-24h from fertilisation.  The eggs (155-200µm) are rusty-brown in colour, but change to light green after a few minutes in the ocean.  A non-feeding veliger larva is reached within 2-3d, and is still planktonic. By 6-7D (160h in the figure on the Right) the larva is crawling on the substratum and, by 5-10d, depending upon temperature, metamorphic competency is reached.  Within a day the post-metamorphic juvenile is feeding on diatoms.  By 40d the juvenile is about 1mm in length.   Combined data from Fritchman 1961 Veliger 3: 95; Fritchman 1962 Veliger 4: 41,134; Koppen et al. 1996 Veliger 39: 241, Holyoak et al. 1999 Veliger 42: 181; Kay & Emlet 2002 Invert Biol 121: 11.  Drawings of developmental stages adapted from Kessel 1964 Biol Bull 127: 294 for Atlantic-coast Acmaea testudinalis.

NOTE  the times listed here are variable because the data are drawn from several publications dealing with different species raised at different temperatures. The general pattern shown in the drawings on the Right are for Acmaea testudinalis (Atlantic coast) cultured at temperatures of about 20^OC

Studies on Lottia digitalis at Cape Arago, Oregon show that spawning occurs between Feb-Apr.  Of 3 spawnings observed by the author in a 2-yr period (one of these is shown in the figure on the Left), all occur during, or within a day of, high storm surge.  The on-shore winds that produce the surge also create near-shore downwelling, which is likely to sweep the larvae offshore.   A few days later, as a result of reversal of wind direction, the downwelling is replaced by upwelling, which could theoretically bring the larvae back onto the shore, perhaps just at the onset of metamorphic competency.  Shanks 1998 J Exper Mar Biol Ecol 222: 31.

NOTE spawning is assessed from abrupt change in gonadal state. Gonadal state or "gonad index" is categorised into 6 stages ranging from Stage 0 where the gonads are so poorly developed that it is difficult to determine an individual's sex, to Stage 5 where 75% or more of the visceral mass is represented by gonads

Lottia gigantea

Unambiguous demonstration of protandry in a limpet, or any animal, requires that gonad size be monitored over time in an individual.  However, data from single collections, such as shown here for the owl limpet Lottia gigantea from San Nicolas Island, California are certainly suggestive. Note in the graph that small individuals are mostly of indeterminate sex; intermediate-sized individuals are mostly males; and large individuals are mostly or all females.  However, as noted by the authors, for irrefutable proof a change in sex over time in a single individual is required.  This is tested by first locating 30 males, numbering their shells with epoxy glue, and releasing them into their habitat on San Nicolas Island.  Fourteen months later a search in the same area of shore yields 9 numbered individuals, 5 of which are still males, but the remaining 4 of which have changed to females.  The authors conclude that not only is Lottia gigantea protandrous, but that an individual can change sex over a single breeding season.  Wright & Lindberg 1982 J Mar Behavior UK 62: 737. Photo courtesy Jackie Sones, Bodega Marine Laboratory, California.

NOTE  identification of sex is accomplished non-lethally by sampling the gonads with a hypodermic syringe through the rear body wall 

Sex change in owl limpets Lottia gigantea may be environmentally mediated.  When male limpets at San Nicolas Island, California are kept in large enclosures¹ (representing a low-density treatment) and kept for 1yr, they change to females at a significantly higher rate (69%) than ones kept in small² enclosures (representng a high-density treatment and leading to 10% sex change; see histogram).  In addition, large males are more likely to change sex than small ones.  It seems that each limpet’s territorial status prior to the experiment may have been an important component of this size effect.  Thus, a dominant territorial status correlates with an individual’s size and therefore its potential egg-producing capacity³ (as a female), and hence may be a good cue for initiation of sex change.  Finally, low density may be a correlate of high mortality and, therefore, may also be an adaptive cue for sex change.  The author notes that the data here confirm an earlier hypothesis that sex change in L. gigantea can be environmentally mediated. Wright 1989 Mar Biol 100: 353; see also Lindberg & Wright 1985 Veliger 27: 261.

NOTE¹  the limpets are actually kept as pairs in ring-enclosures.  The enclosures are of such a size as to mimic the extremes of natural densities.  Thus, a small ring-enclosure of 0.02m^-2 is equivalent to a field density of 100 individuals ^. m^-2, and a large ring-enclosure (0.2m^-2) to 10 individuals ^. m^-2

NOTE²  does the more frequent shell-bumping in the small enclosures mimic the presence of other competitively dominant individuals and thus inhibit sex change?  The author addresses this point by noting that all the contained limpets (in both large and small rings) exhibit a strong territorial response to other limpets introduced at the end of the 1-yr period

NOTE³  the author calculates that a 75mm shell-length limpet has a tenfold greater egg-producing capacity than a 50mm one

In the Monterey Bay area limpets Lottia limatula spawn in late winter. Markel 1974 Physiol Zool 47: 99.

Lottia scabra in the Monterey Bay region of California is ovigerous from late Aug to mid-Jan and larvae settle in winter/spring.  By July, this cohort has attained 8-12mm in size. The author notes that of 465 individuals of adult size (20-30mm shell length) assayed on one collection, 392 or 84% are female.  Protandry, that is, sexual development in which individuals start off as males then change to females at a later age, is known for a few world species of limpets (e.g., Patella spp.), and has been described for west-coast Lottia gigantea. This early observation on L. scabra seems not to have been investigated by later researchers. Hewatt 1940 Amer Midl Nat 24: 205.

NOTE  lit. “first male” G.

Lottia scabra in the region of Bodega Head, California, begin to build gonads in August and are "ripe" by mid-November.  Spawning is in January-March.  Although comparative data are available for just one spawning season, individuals at higher levels on the shore appear to show more seasonal “regularity” in spawning than individuals just 0.5m lower on the shore.   Note in the figure the greater number and more spread-out spawning events during the 1968 season in the lower-zone population.  Sutherland 1970 Ecol Monogr 40: 169.

NOTE  the HIGH and LOW levels on the shore shown in the graph are 1.7m and 1.2m above MLLW, respectively

Despite the common occurrence of keyhole limpets Diodora aspera on west-coast shores, practically nothing is known about the species’ reproductive cycle.  A brief mention in a paper on a related fissurellid, the giant keyhole limpet Megathura crenulata, suggests that Megathura may be a year-round dribble-spawner.  Beninger et al. 2001 J Shellf Res 20: 301.

NOTE  the paper provides much information on gonad and gamete structure, and the nature of vitelline reserves in Megathura, but no information on Megathura’s reproductive cycle other than the possibility of dribble-spawning. The study is done in France on a single collection of specimens from Long Beach, California 

Giant keyhole limpet Megathura crenulata on the under-
surface of a rock. Co-inhabitants of the rock surface
are colonial tunicates, bryozoans, and tubeworms 1X